Organic Light Emitting Diode (OLED) is a flat panel display technology which has great prospects for development. It possesses extremely excellent display performance, and particularly the properties of self-illumination, simple structure, ultra thin, fast response speed, wide view angle, low power consumption and capability of realizing flexible display, and therefore is considered as the “dream display”. Meanwhile, the investment for the production equipments is far smaller than the TFT-LCD. It has been favored by respective big display makers and has become the main selection of the third generation display element of the display technology field. At present, the OLED has reached the point before mass production. With the further research and development, the new technologies constantly appear, and someday, there will be a breakthrough for the development of the OLED display elements.
The OLED comprises an anode, an organic emitting layer and a cathode sequentially formed on a substrate. The respective functioning material layers and the cathode metal layer of the OLEDs are manufactured by vacuum thermal evaporating process. The vacuum thermal evaporating process needs the usage of the mask plate. The function of the mask plate is to evaporate the OLED material on the designed locations. Therefore, the aperture location, the shape and the surface planeness of the mask plate are significantly important. FIG. 1 is a diagram of an OLED material vacuum thermal evaporating process. The OLED material 200 for evaporation is put inside the crucible 100. In a vacuum environment which is smaller than 10−5 Pa, the temperature of the crucible 100 slowly ascends. After reaching the gasification temperature of the OLED material 200, the OLED material 200 becomes gas and sublimates to pass through the aperture of the mask plate 300. The gas molecules are deposed on the surface of the substrate 400, and become solid state molecules as temperature descends. Molecules of OLED material constantly accumulate and slowly form a thin film on the substrate 400.
Please refer from FIG. 2 to FIG. 6, which are diagrams of manufacture process of an OLED material vacuum thermal evaporating mask plate according to prior art. The manufacture process generally comprises: step 1, as shown in FIG. 2, manufacturing a stainless mask frame 10; step 2, as shown in FIG. 3, providing a mask substrate 20′, and the mask substrate 20′ is a stainless or ferro-nickel steel thin sheet with a thickness of 50 micrometers or 100 micrometers; step 3, as shown in FIG. 4, patterning the mask substrate 20′, i.e. opening some small apertures 21 on the mask substrate 20′ to form a mask 20; step 4, as shown in FIG. 5, applying a certain force around the mask 20 to make the surface to be flat, and the apertures 21 do not deform. Then, the mask 20 and the mask frame 10 are aligned; step 5, as shown in FIG. 6, the mask 20 and the mask frame 10 are welded by laser welding. After the aforesaid manufacture process is accomplished, the surface of the mask 20 is flat. The aperture 21 does not deform and the mask 20 can be easily handled with moving the mask frame 10.
After a certain usage duration of the mask, the OLED material with a certain thickness is deposed thereon, the mask can easily droop and deform with gravity, and the OLED material may block apertures or shrink the effective dimension of the apertures. After the certain usage duration, the mask needs cleaning and even replacement of a new one.
When a new mask is required for replacement, the original mask has to be separated from the mask frame. The mask is removed, and the mask frame surface is ground and polished. The original point weld location should have emboss and the mask frame surface needs to be ground to be a plane (the planeness is less than 50 micrometers) Meanwhile, in the original point weld location, the heat of welding is equivalent to a thermal process to the welding point, which can cause the hardness of the point weld location gets higher. This hardened layer also requires grinding to remove so not to influence the point weld result of the next mask.
Under such circumstance, after replacing the mask many times and the mask frame has been polished many times, the thickness will gradually become thinner, which not only influences structure strength of the frame but influences also the alignment location of the mask in the evaporating apparatus. Therefore, the mask frame needs to be wasted after grinding and polishing with a certain thickness, and the mask frame needs to be conveyed to the factory having a large polishing grinder for grinding and polishing. The time is wasting. Thus, many spare mask frames are essential and the production cost increases.